The invention relates to a method for controlling a yarn processing system and a yarn processing system. xe2x80x9cYarnxe2x80x9d is intended to comprise not only conventional textile or synthetic yarn material, but predominantly a longitudinally extending substrate of high tensile strength like a tension resistant carbon or aramid fibre, a metal wire, or the like.
For the production of functional reinforcement, fabric yarn material is processed which is tension resistant and optionally apt to stand high loads. For example, for filtering or bossing fabric webs used in paper and cardboard machines, W warn material is woven having very high tension resistance. Significant problems occur when handling such yarn materials in a conventional manner between the supply spool and the yarn feeding device with overhead yarn release from the supply spool.
It is an object of the invention to provide a method of the kind as mentioned above as well as a yarn processing system which allows processing of yarn material of particular tensile strength and extreme strength without problems.
According to the method of the invention, problems otherwise occurring due to an overhead release of the yarn from the supply spool are eliminated by tangentially releasing the yarn from the supply spool. In this case the winding drive of the yarn feeding device is producing the yarn tension necessary for rotating the rotatably provided supply spool. The yarn enters the yarn feeding device properly and without twist as dictated by the rotation of the winding drive. The rotatably provided supply spool allows the winding drive to precisely release the yarn amount needed per time unit.
In accordance with the system features the rotatably journalled supply spool is positioned such that it allows a tangential release of the yarn by the yarn feeding device. The winding drive of the yarn feeding device is acting as a rotational drive for the supply spool since at least the yarn tension generated by the winding drive as well as the tensile strength of the yarn produce the torque necessary to rotate the supply spool. In this way the problems which otherwise result from the yarn properties are solved surprisingly simply.
Expediently additionally the rotational resistance of the supply spool is regulated actively. This is a significant feature of the method and considers the condition that the winding drive has to be accelerated relatively rapidly to a high speed and at the same time has to drag the supply spool with it, or has to be brought to a stand still relatively rapidly while then the supply spool tends to continue to rotate further. As a parameter for the regulation of the rotational resistance an essentially constant yarn tension can be used. Preferably, the regulation is carried out substantially in synchronism with speed variations of the winding drive. The winding drive provides the necessary rotation of the supply spool, but is assisted by the regulation of the rotational resistance of the supply spool. A respectively regulated decrease of the rotational resistance is felt by the winding drive as a relief. An additional conveying motion of the supply spool assists during acceleration of the winding drive. In case of a stoppage of the winding drive the rotational resistance of the supply spool is increased accordingly to avoid an after run of the supply spool.
Advantageously, the yarn tension is detected and then the rotational resistance of the supply spool is regulated in view of a reference yarn tension. The winding drive constantly fulfils a predetermined drive function for the supply spool. However, the winding drive may be assisted in its driving function in a positive or a negative sense, when the rotational resistance of the supply spool is regulated accordingly.
The rotational resistance of the supply spool can be decreased by active rotation of the supply spool, however, exclusively to a degree by which it is assured that the winding drive permanently has to pull, but that the yarn is not relaxed.
Particularly expediently the rotational resistance of the supply spool is increased by active braking of the supply spool to a stand still when the winding drive is switched off. In this way an after run of the supply spool is prevented. In order to constantly assure a determined basis yarn tension it is expedient to even bring the switched off winding drive by the yarn itself into a stand still condition by braking the supply spool.
The regulation of the rotational resistance of the supply spool either is carried out with the help of yarn sensor signals or by means of run or stop signals representing the current actuation of the winding drive, i.e. under consideration of the actuation current or a current free condition of the winding drive.
In a simple variant of the method, the rotational resistance of the supply spool is only varied between a free running condition in the rotational journalling of the supply spool and a complete stand still. The supply spool is stopped actively as soon as a yarn sensor signal occurs which results in the stop of the winding drive or when the actuation current of the winding drive is switched off.
In this case the supply spool expediently is brought to stand still with an adjustable deceleration in order to keep the mechanical loads of the yarn, the yarn feeding device and also the supply spool low.
When switching on the winding drive, a decrease of the rotational resistance of the supply spool can be controlled when switching on or even a little earlier.
In the system it is expedient to equip the supply spool with a device for varying its rotational resistance. The device then is responsible for the acceleration or the stoppage of the supply spool, respectively, in case that the winding drive in the yarn feeding device is not capable of carrying out these tasks. This may happen during acceleration of the supply spool, however, mainly is necessary when stopping the winding drive to stop the supply spool.
A slip rotational drive for the supply spool is capable of assisting the winding drive during release of the yarn without adjusting a perfect synchronism, and also is advantageous to decelerate the supply spool to stand still.
For that function the slip rotational drive should be switchable between a conveying operation mode and a braking operation mode.
Since the winding drive due to its additional function as a rotational drive for the supply spool does have a higher input power demand than was necessary for the normal operation of the yarn feeding device, the electromotor of the winding drive and the winding drive itself should be designed for higher power demands than for a normal, only consumption depending operation of the yarn feeding device.
A particularly simple embodiment of the system is using a controlled engageable and disengageable braking device for the supply spool as the device for varying its rotational resistance. In disengaged condition only the natural rotational resistance of the supply spool and its mass inertia are effective. When engaging the braking device the supply spool is braked, preferably to stand still, so that its after run is prevented when the winding drive has to stop.
For engaging the braking device expediently a maximum signal of a yarn sensor is used, or a stop signal of the motor, or a signal, respectively, which is derived from switching off the actuation current.
The braking device can be disengaged as soon as a minimum size signal is generated which also switches on the winding drive, or the run signal of the motor representing the start of the current actuation of the motor. However, it is possible, to disengage the braking device even significantly earlier, namely as soon as the winding drive and also the supply spool have stopped completely.
Expediently, the braking device is engaged with an adjustable deceleration in order to prevent excessive mechanical loads by a too early stoppage of the yarn when the winding drive still carries out an after run motion.
A structurally simple braking device is provided which includes a friction element acting on a braking element of the supply spool, which friction element is adjustable by a controlled driving device. For this function a pneumatic cylinder with or without a spring accumulator, a magnetic brake, an eddy current brake, or the like, may be employed.
Particularly expediently the run signal or stop signal, respectively, of the motor of the winding drive is detected without a galvanic connection and contactlessly by means of an external pick-up head which is positioned at the housing of the yarn feeding device such that it e.g. can detect the current actuation or the current free condition or the presence of a rotating motor magnet field, by using the usual insufficient shielding at such yarn feeding devices against exiting electromagnetic fields, or the like.
The system preferably is used for processing yarn material having high tensile strength like carbon fibres or the like processed for the production of functional reinforcing fabrics.